Just to correct my earlier post, it's the phasing of the Sydenham Rise/London Road lights.

I went for a walk into FH at 5.30 and the level of traffic at Devonshire Road/Dartmouth Road/London Road are at weekday peak levels which is all snarled up. However if you go past Sydenham Rise into Dulwich, the road is mainly clear from FH. Towards FH, it's snarled up from just past Dulwich Library.

It could be a badly phased pattern considering it's been half term for the last two weekends, which revert to normal from tomorrow. As Michael mentions, the weekday phasing is normal.